Combined stabilization ponds–constructed wetland system Original Research Article

In a pre-existing wastewater treatment pilot plant consisting of three interconnected waste stabilization ponds –a facultative pond followed by two maturation/aerobic ones – and located in Sindos near Thessalonica, Northern Greece, we introduced eight vertical flow constructed wetlands, identical in couples, that differ in substrate and plant presence and are fed from the outflow of the first maturation pond. This resulted in the creation of a combined waste stabilization ponds–constructed wetland system, which was being monitored systematically for 2 years in order to study its operation. The unit was fed with septage. The monitored parameters were BOD5, pH, conductivity and TSS. This article presents the results obtained from the aforementioned unit, which are juxtaposed to results recorded in the literature for systems with similar characteristics, before focusing on the differences recorded in the results due to the different characteristics of the wetlands (different substrates, presence or absence of plants). To evaluate the system efficiency, results obtained from the constructed wetlands are compared to respective results recorded from the second maturation pond located in the unit, the inflow of which is the same as that of the wetlands. The constructed wetlands that were left unplanted were the ones which exhibited the highest BOD5 and TSS removal and the lowest conductivities.